Abstract
Climate change is predicted to hamper crop production due to precipitation deficits and warmer temperatures inducing both water stress and increasing herbivory due to more abundant insect pests. Consequently, crop yields will be impacted simultaneously by abiotic and biotic stressors. Extensive yield losses due to such climate change stressors might, however, be mitigated by ecosystem services such as insect pollination. We examined the single and combined effects of water stress, insect herbivory and insect pollination on faba bean yield components and above‐ and belowground plant biomass under realistic field conditions. We used rainout shelters to simulate a scenario in line with climate change projections, with adequate water supply at sowing followed by a long period without precipitation. This induced a gradually increasing water stress, culminating around crop flowering and yield formation. We found that gradually increasing water stress combined with insect herbivory by aphids interactively shaped yield in faba beans. Individually, aphid herbivory reduced yield by 79% and water stress reduced yield by 52%. However, the combined effect of water stress and aphid herbivory reduced yield less (84%) than the sum of the individual stressor effects. In contrast, insect pollination increased yield by 68% independently of water availability and insect herbivory. Our results suggest that yield losses can be greatly reduced when both water stress and insect herbivory are reduced simultaneously. In contrast, reducing only one stressor has negligible benefits on yield as long as the crop is suffering from the other stressor. We call for further exploration of interactions among ecosystem services and biotic and abiotic stressors that simulate realistic conditions under climate change.
Highlights
Agricultural crop production is expected to be increasingly affected by weather patterns associated with climate change, such as more frequent prolonged dry periods (Lesk et al, 2016; Rosenzweig et al, 2001; Seneviratne et al, 2012)
We examined the single and combined effects of water stress, insect herbivory by aphids and insect pollination by bumble bees on faba bean yield components and above- and belowground plant biomass under realistic field conditions
The fact that the interaction between water availability and insect herbivory was already present for flower abundance and was maintained to crop yield, illustrates that the interaction between water availability and insect herbivory for plant reproduction was established at an early plant growth stage
Summary
Olesen et al, 2011). In addition, crop yields in temperate regions are predicted to be increasingly impacted by insect herbivory as a warming climate promotes insect pest population growth, consumption rates (Deutsch et al, 2018; Lehmann et al, 2020) and range expansion into cooler, hitherto unsuitable regions (Bebber et al, 2013). Switches in bee foraging behaviour are associated with pollen and nectar availability, where legitimate pollination increases when pollen abundance and quality are high (Marzinzig et al, 2018; Poulsen, 1973) It remains unknown if water stress or insect herbivory trigger behavioural shifts that indirectly affect crop yield by altering foraging behaviour. We used rainout shelters to simulate a scenario with adequate water supply at sowing, followed by a long period without precipitation, in line with climate change projections This gradually increasing water stress over the growing season culminated around flowering and early pod-fill, when the crop is most sensitive to reduced water availability (Daryanto et al, 2015; Karkanis et al, 2018). We hypothesized that the insect pollination benefit to yield (kg/ha) is less pronounced in plants suffering from water stress and insect herbivory than in healthy plants, due to reduced pollinator visitation and a behavioural shift from legitimate flower visits to nectar robbing
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